The present invention pertains to the field of the steering of land vehicles, in particular of motor vehicles provided with a mechanism of assisted steering or power steering.
Conventionally, motor vehicles are provided with a chassis, a cabin, wheels linked to the chassis by a suspension mechanism with front steered wheels controlled by a steering wheel at the disposal of the driver in the cabin of the vehicle. Between the steering wheel and the ground wheels is provided a steering column rotationally secured to the steering wheel whose lower end is provided with a pinion acting on a rack, making it possible to rotate the ground wheels about a substantially vertical axis, so as to ensure their orientation and the rotation of the chassis of the vehicle.
Such steering mechanisms may be hydraulically or electrically assisted so as to reduce the driver effort, in particular during maneuvers to a halt, for example, a parking maneuver.
More recently, power steering arrangements have appeared comprising a sensor of the angular position of the steering wheel mounted some distance from an actuator acting on the rack as a function of the angular position detected by the sensor to which it is linked by a wire link.
Document U.S. Pat. No. 5,884,724 describes a steering arrangement with variable geardown ratio, with maintaining of a constant geardown ratio for a few instants during a dynamic maneuver so as to avoid disturbance to the driver. The geardown may be small at low speed so as facilitate the maneuvering of the vehicle that one seeks to park.
However, the applicant has realized that a judicious refinement of the steering mechanisms made it possible moreover to increase safety and improve the road holding of the vehicle. Hitherto, the improvement in the road holding of the vehicle was obtained through an increase in the rigidity of the chassis, an improvement of the tires or else better adjustment of the suspension.
Now, the delay time between the action of the driver on the steering wheel and the commencement of the turning of the vehicle is variable from one vehicle to another. In certain driving cases, the delay time may be prejudicial, or even dangerous. During an avoidance maneuver at average speed, a driver with average training will give an abrupt tug on the steering wheel of large amplitude. The amplitude given by the driver is increased if the driver feels that the vehicle is not turning immediately. At this moment, the vehicle begins to turn and may deviate significantly from the trajectory desired by the driver who reacts by counter-steering so as to put the vehicle back on line. The counter-steering of the driver may again be excessive. The de-phasing may be dangerous at that moment by rendering the vehicle unstable through a phenomenon of antinomy between the tugs on the steering wheel and the response of the vehicle.